An important aspect when wearing shoes is that the shoe should be comfortable to wear. Elements that can increase the comfort of wearing a shoe includes flexibility of the shoe sole and another aspect may be the softness of the surface inside the shoe having contact with the surface of the foot wearing the shoe.
Normally, the comfort of a shoe is optimized by having specific properties of the sole material, but sometimes a specific sole material needs to be used due to design requirements or the type of shoe or due to the type of shoe determining specific design elements.